1. Field of the Invention
The invention relates to ground-fault interrupter systems and, more particularly, to the sensing of the grounding of electrical equipment. Still more particularly, the invention relates to a system for discontinuing power to electrical equipment when grounding of the equipment is interrupted.
2. Description of the Prior Art
Ground safety controllers are used to offer protection against anomalous electrical conditions which may arise, for example, when an electric voltage is impressed upon equipment with respect to the ground. If there is ineffective grounding, a dangerous electrical shock can result which may cause injury or death.
Various devices to interrupt power are available to prevent such incidents. They generally include differential amplifiers, transformers or similar systems. Usually, however, such systems operate only after the fault situation has occurred. A variety of ground-fault indicator or interrupter circuits are disclosed in the prior art. For example, an invertor-type ballast with built in differential current transformer to sense substantive differences in currents flowing from each of two output terminals is disclosed in Nilssen U.S. Pat. No. 4,855,860. Wilson U.S. Pat. No. 4,093,977 discloses a self powered, self-contained ground fault protective device with a circuit for monitoring ground fault current and a ground integrity monitor for an electric apparatus is disclosed in Volk, Jr., U.S. Pat. No. 3,996,496.
It is desirable to provide a system in which total disablement of the equipment occurs if a true earth ground is absent and for immediate interruption of equipment functions if electro-magnetic interference is generated.